Process of maxing esters



Patented Sept. 3, 1929.

Ul ilTED HYYM E. BUG, F ROSELLE, AND WOODMAN W. GLOUGH, OF ELIZABETH, NEW JERSEY,

ASSIGNORS TO STANDARD DEVELOPMENT COMPANY, A CORPORATION OF DELA- WARE.

PROCESS OF MAKING ESTERS.

3V0 Drawing.

This invention relates to the art of making esters, and will be fully understood from the following description.

In the customary process of making esters,

5 the alcohol and organic acid to be esterified are heated with a large quantity of sulfuric acid. While satisfactory for primary alcohols, if this process be attempted with secondary and tertiary alcohols the result is an ex- 1 tensive breaking up of the alcohol itself.

In the present invention, such alcohols particularly those of more than three carbon atoms are dealt with, as can be readily esterilied, and with the output of products of excellent purity.

The features of the invention will be brought out by referring to an illustrative example:

About 55%of commercial secondary butyl alcohol, that is, the alcohol as it comes from the finishing run and without total dehydration, is mixed with about 45% of strong acetic acid; the acid need not be glacial acid, but preferably will be of at least 75% concentration. It will be understood that much more water in the acid would not be a bar to operation, but unless there is some other'object to be gained by the use of dilute acid it is not very profitable, since it makes that much 0 more water for the esterification still to get rid of, and correspondingly holds down capacity at this point. Along with the esterification components, it ordinarily pays to add a suitable catalyst. This may be any strongly ionizable acid in small amount, not to exceed 0.5%, for instance concentrated sulfuric is convenient and may be used preferably 0.1% in amount by volume on the total charge of esterification components.

4 The mixture, in a still fitted with a suitable fractionating column, is now subjected to distillation, and the distillate is collected and allowed to stratify. The lower layer is largely water. This may be run into a waste drain if desired, or preferably it may be run to storage to be ultimately worked up to recover I what alcohol it carries; The upper layer of the condensate contains alcohol and secondary butyl acetate and is resubjected to the distillation. This may be done continuously or intermittently as desired. Preferably this layer is simply refluxed back to the distillation vessel by a suitable run-back line. Proceeding on in this way, refluxing back to the l stil the alcohol and ester distilled over, that Serial No. 658,899.

is, the layer of the condensate comprising substantially all of the organic material, and running away the water portion of the condensate, the water of esterification is continuously eliminated as the esterification proceeds, until the end point is reached, which is shown by the lack of suficient water in the condensate to allow the Stratification.

The content of the still is now largely ester, with some alcohol and acetic acid, and the ester can be separated out as desired. A preferable procedure is, when the stratifying of the condensate in the collector practically ceases, to discontinue the refluxing and then distill the still contents until the temperature shows within a few points of the boiling point of secondary butyl acetate. This distillate or heads as it may be called, contains alcohol and a small amount of acid and some ester, and may be advantageously added to the next batch charge. Distillation is further contin ued up to two or three degrees of the boiling point of acetic acid. The residue in the still is used again in the next batch operation. The distillate which consists mainly of ester, but containing 15 to 30% of acetic acid is now subjected to fractional distillation after adding water sufficient to form a constant boiling point mixture with the secondary butyl acetate.

If desired, this fractional distillation with water could be carried on from the original still but in that case the acidity due to the mineral acid catalyst must be destroyed. For this a convenient way is to add some suitable salt of acetic acid or of some other weakly ionized acid of suitable properties.

If the water fractionation is carefully done the ester 'is brought over with very little acetic acid, and the acetic acid left is strong, and well suited to go into the next operating batch. The distilled ester can be further purified by washing with water, and if necessary treating with sodium carbonate, anddrying over a salt and redistilling as is usual.

Instead of starting with the proportions of secondary butyl alcohol and acetic acid mentioned in the foregoing example, the proportions can be widely varied, for instance 10-50% of acetic acid and the balance alcohol.

Similar examples, using other commercially'usefulalcohols of more than three carbon atoms, for instance secondary amyl alcohol, iso-amyl alcohol, and hexyl alcohols, andalso combinations Wlth other acids above ferrule,

that close limitation to molecular proportions in the charge of the components is not required, but considerable latitude for either component is possible. Also, anhydrous materials are not required, but as much extra water may be worked out as may be found desirable, all factors considered. Continuous features of operation may be embodied by providing suitable feed, and series stills.

We claim:

. 1. A process of making secondary butyl acetate, which comprises subjecting to distillation a mixture of secondary butyl alcohol about 55%, strong acetic acid about 45%, and concentrated sulfuric acid about 0.1%, allowing the condensate collected to stratify into layers, and continuously refluxing the upper layer, discontinuing the refluxing when stratification practically ceases, and distilling off the still contents up to within'a few points of the boiling point of secondary butyl acetate, then further distilling up to two or three degrees of the boiling point of acetic acid while separately collecting the distillate, adding water to this distillate to form a constant boiling mixture with the secondary butyl acetate present, and distilling off the aqueous secondary butyl acetate.

2. A process of making secondary butyl acetate, which comprises subjecting to distillation a mixture of secondary butyl alcohol, acetic acid and less than 0.5% of a highly ionizable mineral acid, allowing the condensate collected to stratify into layers, refluxing the upper layer, discontinuing the refluxing when Stratification practically ceases, then 'further distilling off the still contents to almost the boiling point of secondary butyl acetate, then further distilling up to two or three degrees of the boiling point of acetic acid, while separately collecting the distillate, adding water to this distillate, and distilling off the secondary butyl acetate. 1 3. A process of making esters, which comprises subjecting to distillation a mixture of an aliphatic alcohol containing more than three carbon atoms and an aliphatic acid containing more than one carbon atom in the contents the ester in mixture with acid, adding water to the mixture, and distilling off the ester.

4. In a process of making esters of alcohols other than primary alcohols. the improvement which comprises mixing, in the absence of any chemical having a substantial dehy-' drating effect, the corresponding aqueous alcohol and an aliphatic acid capable of forming therewith an ester relatively insoluble in water, distilling the mixture in the presence of a small percentage of an acid catalyst to form a distillate containing esterified material and water. condensing the distillate, allowing the condensate to stratify, whereby the esterified material separates substantially completely from the water, withdrawing the water, returning the layer containing said esterified material to the mixture undergoing distillation, and recovering the esterified material.

5. A process of making esters, which comprises subjecting to distillation in the pres ence of an acid catalyst, a mixture of an alcohol and an acid yielding an ester-containing condensate capable of stratifcation, said mixture being at no time in contact with a chemical having a substantially dehydrating effect, allowing the condensate collected to stratify. returning the layer containing the greater proportion of esterified material to the distillation vessel, and recovering the ester.

6. A process of making esters,.which comprises subjecting to distillation in the presence of an acid catalyst, a mixture of an alcohol and an acid yielding an ester-containing condensate capable of Stratification, said mixture being at no time in contact with a chemical having a substantially dehydrating effect, allowing the condensate collected to stratify, and further working up the layer containing the greater proportion of esterified material.

7. A process of making esters, which comprises subjecting to distillation in the presence of an acid catalyst, a mixture of an alcohol and an acid yielding an ester-containing condensate capable of Stratification, said mixture being at no time in contact with a chemical having asubstantially dehydrating effect, allowing the condensate collected to stratify and recovering the ester.

HYYM E. BUG. WOODMAN W. CLOUGH. 

